Chris Pratt and Katherine Schwarzenegger Make Their Relationship Instagram Official

Chris Pratt and Katherine Schwarzenegger made their relationship official on Thursday.

The Guardians of the Galaxy actor posted a collage of photos of himself and his 29-year-old girlfriend for her birthday. In his caption he gushed about the birthday girl, writing that she "lights up the room."

Pratt's collage included photos of himself kissing Schwarzenegger, a picture of her giving him a pedicure and a snapshot of the couple sporting animal sheet masks. It also included three candid photos of Schwarzenegger smiling.

Their relationship, which dates back to around June, is heating up, a source recently toldET Online. They're said to be in a "serious relationship and everything is going well." Don't expect to see these two planning a wedding anytime soon, however.

"Chris just finalized his divorce from Anna [Faris] a couple months ago, and he's happy with just dating Katherine for now. The couple has a lot of fun together and is fully involved in one another's life," the source said, adding that they're "in a committed relationship. There just isn't a rush to take it to the next step right now. Chris is enjoying the dating process."